Method of determining leaks from buried pipelines using a time-sharing transmission line

ABSTRACT

A method of determining leakage from a buried pipeline using a closed-loop radar system having time-sharing transmission line buried adjacent to the pipeline to be monitored.

United. States Patent Frederick Alexander Roberts Bren; Edwin D.Saunders, Whittier, both of, Calif.

[72] I Inventors 21 1, App1.No. 812,676

2,056,085 9/1936 Alles 34o/23sx T'RANSI-CEIVER 2,387,783 Tawney 10/1945333/96 X 2,759,175 8/1956 Spalding.... 340/235 X 2,794,071 5/1957 Hugheset al. 324/52 X 2,843,668 7/1958 llgenfritz 324/52 X 3,195,079 7/1965Burton et al.. 333/95 3,205,462 9/1965 Meinke 333/95 3,345,450 10/1967Spindle 333/96 X 3,382,493 5/l96 8 Loper et a1. 340/235 X 3,435,08512/1969 Hawkins... I 73/405 X 3,510,762 5/1970 Leslie 324/52 PrimaryExaminer-Gerard R. Strecker Attorneys'A. L. Snow, F. E. Johnston, R. L.Freeland, Jr. and

Harold D. Messner ABSTRACT: A method of determining leakage from aburieu pipeline using a closed-loop radar system having time-sharingtransmission line buried adjacent to the pipeline to be monitored.

SWITCH l' T'l- Z5 r l J REFLECTOMETER OSCILLOSCOPE PATENTED we I 7 I971SHEET 2 [1F 2 INVENTORS F. ALEXANDER ROBERTS EDWIN 8. SAUNDERS gyjg/m/oy/1d ATTORNEYS METHOD OF DETERMINING LEAKS FROM BURIED PIPELINES USING ATIME-SHARING TRANSMISSION LINE This invention relates to a method ofdetermining the location of leakage from a buried pipeline irrespectiveof whether or not the pipe is capable of conducting an electric currentor magnetic flux and pertains more specifically to detecting andrecording leakage from buried pipes (which, in addition to beinginaccessible from outside of the pipe wall, may also carry nonaqueous,hostile liquids that render testing from inside the pipe undesirable) byuse of a closed-loop radar system including a time-sharing transmissionline buried adjacent to the pipeline to e monitored. The invention hasspecial utility in monitoring pipeline activities carried out in thepermafrost zones of the world such as Alaska and Canada. (permafrostregions are defined as the perennially frozen layers of earth formationwhich have remained below C. for many years.)

Pipelines, and particularly buried pipelines associated with conveyanceof petroleum products, undergo corrosion. Heretofore it has been normalin monitoring buried pipelines to wait until leaks have actuallyoccurred before thepipeline is serviced. For example, as these leaksmanifest themselves as seepage at the earth's surface an inspector candetect them and initiate action for replacement of the corrodedpipeline. However, it is evident that there is a time lag between theactual emission of the liquid from the pipes and its appearance at theearths surface. The time required for the liquid to flow to the earth'ssurface may be quite long depending on the stratigraphy of the earth inthe region where the leak occurs, Accordingly, large amounts of liquidmay be lost before the leak can be actually detected and the pipelinerepaired. Further, the time lag between emission of the liquid and itsappearance at the earth's surface may create substantial health andpollu tion hazards.

With respect to buried pipelines, visual inspection is, of course, notpossible. Attempts in the prior art to inspect buried pipelines usingremotely situated electric, magnetic or radioactive inspection systems,have been unsatisfactory due, primarily, to their inability to providean accurate and rapid indication of the location of flaws, especiallywith respect to known geographical points. Where the piping structure isburied, the earth itself exerts a shielding effect. Conventionalinspection systems are not only affected by varying soil conditionsadjacent to the pipeline that is monitored, but also the presence ofplant life or the use of manmade protective surface barriers, such aspavement, also contribute adversely to the detection of flaws withinburied pipelines. Further, in many cases it is not practical to reducethe shielding effect of the earth by boring large numbers of test holesalong sections of the pipeline.

Where the buried pipeline is coated with a protective layer of plasticsmaterial or the like to prevent corrosion, the shielding effect of theearth on conventional audio detection systems may be even morepronounced. in audio detection systems, after the coated pipe has beenplaced in a trench and covered with soil, a characteristic audio signaldeveloped along the pipe is monitored by an operator walking along theearth above the pipeline. As a flaw in the pipeline is approached, theoperator detects a variation in signal strength. A successful detectionsystem should be capable of rapidly and accurately inspecting relativelylong lengths of pipe for flaws, however, and provide an accurate recordof the flaws by means of a record which can provide accurate correlationwith the actual pipeline. A successful system should also havetime-sharing capabilities with other functional equipment since use ofthe detection system is usual on a periodic (say weekly) operationalbasis. This is especially true where the pumping and discharge terminalsof the pipeline to be monitored are separated by long distances ofpennanently frozen land areas such as found in northern regions ofAlaska and Canada In such environments the remoteness of theoilproducing sites from the discharge terminal, the extremely lowtemperatures, and the varying atmospheric conditions, dictate that adirect-linked communication system, in addition to the usual radiosystems, is highly desirable.

In accordance with the present invention, a rapid and accurate method ofinspecting buried pipelines (coated or otherwise) for flaws and locatinglocations of leakage of liquid from the pipeline is achieved by theprovision of a closed-loop radar system including a time-sharing coaxialtransmission line buried in an adjacent location to the pipeline to bemonitored. The present invention contemplates that before the pipeline(coated or otherwise) is placed within a trench, or buried at thesurface of the earth, the coaxial transmission line is buried at a depthbelow the pipeline. Vertical spacing therebetween, if any, remainssubstantially constant along the pipeline/transmission line link.Preferably the coaxial transmission line and the pipeline are buries sothat as the pipeline develops flaws, the liquid leaking from thepipeline quickly seeps into contact with the outer cover of thetransmission line. The outer covering of the coaxial transmission lineis formed of a material that can be easily penetrated by the liquidbeing transported within the pipeline. Thus, if oil or petroleumproducts are carried in the pipeline, the outer covering of the coaxialline can be formed of asphalt materials, wax-based compositions,rubberbased (oil-soluble) compositions or synthetic (oil-soluble)polymers. After the coaxial transmission line and the pipeline have beenburied, the conductors of the transmission line are connected to areflectometer at the earth's surface, as through a vertically extendingtrunkline. The reflector is conventional in design and detectsdiscontinuities in the coaxial transmission line due to the intrusion ofpipeline liquids. The reflectometer, say operating in the time domainmode, includes a pulse generator triggered by means of a synchronizingsignal from a conventional time base connected to, in turn, andtriggering a sampling oscilloscope. A pulse of electromagnetic energy isdriven through a conventional sampler into the buried coaxialtransmission line and propagates along that line adjacent to the buriedpipeline. As the energy strikes discontinuities along the transmissionline (marking intrusions of liquid), the signals are reflected back tothe reflectometer through the sampler to the oscilloscope. Resultingreflections are displayed on the oscilloscope as anamplitude-versus-time oscillogram. The vertical channel of theoscilloscope is calibrated in terms of reflection coeflicients, thethreshold level being established to detect intrusions into thetransmission line of the liquid of the pipeline. If the liquid withinthe pipeline is an oil or petroleum byproduct, intrusions create highimpedance mismatches along the line so that rather high reflectioncoefficients will be indicated at the display of the oscilloscope.Accordingly, the threshold level, in such applications, of theoscilloscope can be set at a rather high level. Further, rather largelengths of pipeline can e read directly on the horizontal axis of theoscillogram, and correlation of the oscillogram with the actual pipelineis quite easily achieved. A camera may be employed to photograph theoscillogram to provide a permanent record.

The present invention also contemplates that the buried coaxialtransmission line will have a time-sharing capability with conventionalline linked communication systems, these systems coupling, oncommunication, two or more stations along the pipelinetransmission linelink. For example, at one of these stations the reflectometer can beconnected in parallel with a conventional communication system through amultiple-contact microwave switch. Accordingly, when the transmissionline is not being used in the inspection-detection mode, i.e., with thereflectometer system, the communication system can be connected inseries therewith and provide a direct line communication link betweentwo or more stations. Such communication systems are also capable ofdetecting the deterioration in signal strength (as by monitoring signallevel) so as to provide initial indication of increase in reflectioncoefficients along the transmission line due to liquid seepage therein,as from the pipeline. When deterioration in signal strength occurs, theoperator is put on notice of the possibility that leakage from thepipeline has occurred. He can then place in operation the reflectometersystem so that any leakage of liquid from the pipeline can be determinedand the location pinpointed.

It is an object of the present invention to provide a method fordetermining leaks along a pipeline utilizing an electromagneticreflectometer system including a time-sharing transmission linepositioned immediately adjacent to the pipeline and being selectivelycapable of indicating, as reflection discontinuities, intrusions ofliquid seeping therein from the adjacent pipeline, the transmission linealso having time-sharing capabilities to provide a conventionaldirect-linking transmission line for a communication system coupling twoor more stations along the transmission line/pipeline link.

Other objects and advantages of the present invention will be readilyapparent from the following detailed description of a preferredembodiment taken in conjunction with the attached drawings in which:FIG. 1 is a partial section of the near surface of an earth formation inwhich a pipeline has been buried illustrating an electromagnetic leakdetection/communication system of the present invention;

FIG. 2a is a section taken along line 2-2 of FIG. 1;

FIG. 2b is a modification of FIG. 2a in which a coaxial transmissionline of the detection/communication system of FIG. 1 is placed intangential contact with the buried pipeline;

FIG. 3 is an elevational view, partially cut away, of the coaxialtransmission line of FIGS. 2a and 2b;

FIG. 4 is an oscillogram as displayed by the leak-detection system ofFIG. 1 illustrating reflection signal strength as a function of time;

FIG. 5 is a partially schematic, detailed lock diagram of a modificationof the leak detection system of FIG. 1; and

FIG. 6 is an elevational view, partially cut away, of a rectangulartransmission line useful in the system of FIG. 5.

Referring now to FIG. 1, there is shown a hollow pipeline l0 buried intrench 11 at a depth d below surface 12, in earth formation 13. Withinthe pipeline 10, liquids such as oil or oil byproducts are conveyed froma pumping station to a discharge station (not shown) as in the directionof arrow 14. Between the pumping and discharge stations of the pipelinemay be a series of stations (blockhouses) a, b and c as along thesurface 12 of the earth formation 13. Stations a, b and 0 need not belocated directly above axis of symmetry A, of the pipeline but can beoffset from a vertical plane through the axis A varying lateraldistances. Within each blockhouse a, b and c a variety of activities canbe performed. For example, data related to pipeline pumping rates,physical properties of the pumped liquids, etc., can be collected,processed and relayed between stations. Or data can be collected,processed and relayed between stations which is totally unrelated tousual pipeline activities (i.e., payroll calculations, seismic dataprocessing, engineering calculations, etc.)

Pipeline 10, as shown, includes a series of pipe sections 10a, 10b,l0c...10g welded together at a series of joints generally indicated atl6, l7, l8 and 19. After sections of pipeline have been joined andplaced in trench 11, the unburied pipe sections are usually carefullyinspected for flaws. However, after 'the trench has been backfilled andthe pipeline placed in service, flaws may develop, such as at joints l7and 18, due to corrosionalefiects. Liquid seeping from the flaws formspools such as generally indicated at 21 and 22. It is apparent thatpools 21 and 22 constitute operational, health and pollution hazardsthat must be detected as soon as possible. It is also apparent that asuccessful detection system should be capable of performing rapid andaccurate inspection of relatively long lines of pipeline for flaws andof providing an accurate record of the occurrence of seepage from thepipeline as a function of actual pipeline length. A successful systemshould also have time-sharing capabilities related to data collectionand processing functions such as can be carried out at blockhouse a, bor c, and for direct-line communication between the pumping anddischarge terminals of the pipeline. Where the pumping and dischargeterminals are located in remote regions of the world, such as in thepermafrost regions of Alaska and Canada, the need for a direct-linecommunication system, in addition to usual radio systems, is readilyapparent.

In accordance with the present invention, an electromagnetic pipelinedetection-communication system is generally indicated at 25 in FIG. 1.System 25 includes a time-sharing coaxial transmission line 26 buried,in positional alignment with respect to the buried pipeline 10. Beforepipeline 10 is placed within trench 11 (or at the surface 12 in case thepipeline 10 is laid over frozen land as found in Alaska), the coaxialtransmission line 26 is buried at a depth d below the intended depth dof the pipeline 10. After the transmission line 26 and the pipeline 10have been placed in trench 11 in tandem and the trench backfilled,vertically extending trunklines 27, 28 and 29 are connected at one endto the transmission line 26. The junction of the trunklines 27, 28 and29 to the transmission line 26 are indicated at junctions 30, 31 and 32.A closed-loop radar system 33 positioned within each blockhouse a, b andc is attached at the other end of the trunklines 27, 28 and 29.

Radar system 33 operates in the closed-loop mode (closedloop operationindicates direct linkage between the measuring as well as the monitoringsystem), and, as shown, includes time domain reflectometer 36 connectedto transmission line 26 through a trunkline, say trunkline 27, tomicrowave switch 37. Time domain reflectometer 36 is conventional indesign and, in operation, sends a step voltage from a point of knownlocation through a sampler (not shown) into the transmission line 26.The conventional step voltage is generated by a voltage generatortriggered by a time base (both not shown). Electromagneticdiscontinuities in the transmission line 26 due to the intrusion ofpipeline liquids therein, creating impedance mismatches along the line26, as explained in detail below, are detected by measuring themagnitude of the reflected voltage at the reflectometer. Seriallyconnected to the reflectometer is a high-speed sampling oscilloscope 38triggered by the time base of the reflectometer 36. Since the voltagegenerator is preferably transistorized, a good impedance match with alow SO-ohm coaxial line can be achieved without the use of matchingdevices. The oscilloscope 38 is conventional in design and provides fordisplay of reflections of the generated step voltages along thetransmission line 26. The reflected voltage is indicated as a timeprofile at the display of the sampling oscilloscope 38.

Time domain reflectometer 36, useful in the method of the presentinvention, is conventional and can be purchased, for example, from theHewlett-Packard Corp., Palo Alto, Calif. In such applicationsHewlett-Packard time domain reflectometer Model No. TDR-14l5-, forplug-in use with the Hewlett- Packard sampling oscilloscope Model No. A,is preferred. (See technical bulletin entitled HP 140/ 141A Plug-InOscilloscope, July 1967, Hewlett-Packard Corp., Palo Alto, Calif., atpage 28.)

The vertical channel of the oscilloscope 38 is calibrated in reflectioncoefficients for direct readout of impedance mismatch (discontinuities)along the transmission line. No additional vertical or horizontalamplifiers are required. Cathode ray tube display area can be adjustedso as to give maximum resolution of reflected signals. For example,reflection coefficients as small as 0.001 can be observed, correspondingto a standing-wave ratio (SWR) of 1.002. (The standing-wave ratio isdefined as the ratio of maximum to minimum field strength as theposition along the transmission line is varied through a distance of atleast one-half wavelength. Several ways of expressing this ratio havebeen used; usually the ratio of the field strength is expressed directlyas a ratio greater than unity; similarly, the reflection coefficient isusually defined as the ratio of the maximum to minimum field strength ofthe two traveling waves (incident and reflected) traveling along thetransmission line. See Microwave Transmission Design Data, T. Moreno(1948), Dover Publications, Inc., New York, N.Y., at page 20.

Distance can be read directly on the horizontal axis of the oscilloscope38. Distance/time scale on the horizontal axisis calibrated to relatecathode ray tube horizontal length to the actual pipeline length beingmonitored.

Connected in parallel to radar system 33 is transceiver 39 employed tobe alternatively connected to the transmission line 26 by selectiveoperation of microwave switch 3 7. The

transceiver 39 is of conventional design having transmitter and receivercircuits and includes, in its receiver circuit, a meter 40 suitable toindicate variations in amplitude of signals received at the transceiver.When radar system 33 is not in use, the transceiver 39 can utilize, on atime-sharing basis, the aforementioned transmission line, 26. In thisway the transceiver 39 can provide a direct-line communications linkbetween various stations along the pipeline, say between a transmitterwithin blockhouse a and a b in blockhouse b over a preselected timeinterval. Direct" line communications between the pumping and dischargestation of the pipeline can also be maintained. In order that anoperator along the pipeline 10, say at stations a and b, can be awareimmediately of the likelihood of intrusions of fluid from flaws in thepipeline 10, meter 40 is, preferably, constantly monitoring the level ofsignals transmitted from one transceiver and received at anothertransceiver. Meter 40 indicates any decrease in the amplitude of thesignal generated at an adjacent receiver due to losses in thetransmission line connecting the transmitting and receiving transceiversof the adjacent stations. Thus, after entry of the liquid from pipeline10 into the transmission line 26, reflection losses along thetransmission line (caused by impedance mismatches at the point of liquidintrusion) abruptly increase the standing-wave ratio along the line and,correspondingly, decrease the amplitude of the received signal. Such adecrease (below, say, a threshold level) can be used to actuate a soundgenerator such as a horn, bell, siren, etc., through actuation of arelay circuit connected to the sound generator. When deterioration ofsignal strength becomes an actuality, the operator is put on notice ofthe possibility that leakage, of liquid, from the pipeline 10 hasoccurred. Consequently, radar system 33 can be switched into operativeconnection by actuation of microwave switch 37. Such operation of theswitches 37 automatically disconnects the transceiver from contact withthe transmission line.

FIG. 2a illustrates the location of the transmission line 26 withrespect to pipeline 10. As shown, the depth d of the transmission line26 (to its axis of symmetry A is greater than the magnitude of thecombination of the depth d of the pipeline 10 (at its axis A,) below thesurface 12 and outside radius R of the pipeline. Thus, although the axesA and A of the pipeline and the transmission line, respectively, can bealigned in a common vertical plane, their outer surfaces are not intouching contact but are spaced apart by the incremental distance d,where d =d (d+R)-r where r is equal to the outside radius of thetransmission line 26.

However, the pipeline and the coaxial line can be located so thatrespective outer surfaces are piaced in tangential contact as shown inFIG. 2b. In usual applications, the trench 11 is backfilled with soil ofthe original formation which, when compacted, may be rather impermeable;Thus, by placing the transmission line 26' at a distance d, belowsurface 12 (as measured from its axis of symmetry A,') so that its outersurface is in tangential contact with the outer surfaceof the pipeline10', detection of leakage of the fluid from flaws within the pipeline10' can be enhanced. ln the arrangement,

the pipeline 10"is positioned at a distanced below surface 12 asmeasured from its axis of symmetry A,; thus, the depth of thetransmission line d, is equal to d +R+r where R is the outside radius ofthe pipeline 10 and r is the outside radius of the transmission line 26.

FIG. 3 is a side elevation, partially cut away, of a section-oftransmission line 26. As shown, transmission line26 includes a strandedor solid, cylindrical conductor 4 1 surrounded by a coextending helicalouterconductor 42 having a senses of turns42a. The center conductor 41is maintained in fixed position along central axis of symmetry A-by'means of cylindrical, annular insulating spacers 43 periodi'callyspaced therealong. Spacers 43 also aid in establishing an insulating airbarrier between central conductor 41 and outer conductor 42. In turn,outer covering, or sheath 44 of insulating material is placed intangential contact with the outer conductor 42. The impedance andelectrical length of the coaxial line is controlled so that theimpedance per unit length is a fixed value, say 50 ohms per unit length.i

Outer covering 44 must allow intrusion of the liquid (being conveyedwithin the pipeline) so that the liquid can penetrate cavity 49 betweenthe outer conductor 42 and the inner conductor 41 and create an abruptchange in impedance along the line 26. In that way electromagneticenergy propagated along the coaxial transmission line 26 is reflectedfrom the area of the intruded liquid back to a sensing element toindicate the presence of foreign matter within the transmission line.Not only should the outer covering 44 allow intrusion of liquid from thepipeline but it also should exclude all other liquids commonly foundwithin near-surface earth formations, such as ground water. In thisregard, if the liquid within the pipeline 10 is oil or an oil product,outer covering 44 can be formed of asphalt materials, wax-basedcompositions, rubber-based (oilsoluble) compositions or synthetic(oil-soluble) polymers. These materials are soluble within oil or oilbyproducts but are impervious to water. Accordingly, until the outercovering 44 has been penetrated by oil or an oil product, the outercovering 44 remains unflawed and impervious to ground water. The outercovering may be applied in many different ways. For example, the abovematerials may be applied by conventional means as a continuous, uniformcoating. Alternatively, the outer covering may be applied in the form ofan adhesive tape which is composed of a fabric or oil-soluble backingmaterial and an oil-soluble adhesive or gum.

It should also be evident that when the outer cover 44 is intended foruse in permafrost regions, additional types of materials can be employedfor forming the outer covering. Permafrost regions, by definition, areland regions which have remained below 0 C. for many years. Thus, if thetransmission line 26 is placed within a region that is truly apermafrost zone (i.e., the region remains below 0 C.), there is littlelikelihood that ground water can penetrate the outer covering.Therefore, the materials comprising the outer covering need not beimpervious to water. Accordingly, in addition to the materialspreviously mentioned, covering 44 could also be formed of cellulose,-carbowax or guar gum materials. A further advantage of using atransmission line not impervious to water would be to indicate atemperature change along the monitored pipeline. In Alaska, muskeg"areas are defined as areas in the earths surface which, during thesummer months, have temperatures above 0 C. At such temperatures,thawing of the ice within the near surface occurs. Should the pipeline10 be supported at the surface of such muskeg" areas, there is apossibility that rigid support of the pipeline may no longer be possibleas thawing occurs. Thus, if the transmission line is not impervious towater, water entry into the transmissionline can be detectedsimultaneously as the transmission line is monitored'for intrusion ofliquid conveyed in the adjacent pipeline. In that way, the operator ofthe pipeline has been warned of the possibility that the supportstructure of the pipeline may be inadequate.

For application in"muskeg" areas it may be advantageous to employ outercoverings which are specially made to be easily penetrated by both waterand the liquid being transported within the pipeline. These specialcoverings could be made of, for example, emulsifiable wax or asphalticmaterials, conglomerate mixtures of water-soluble crystals or gels andoilsoluble materials, or tapes made'of oil-soluble backing material andwater-soluble adhesive. A furthenexample would consist of covering thetransmission line with alternate spiral wraps of oil-soluble tape andwater-soluble tape.

FIG. 4 is an oscillogram, generally indicated at 45, of the oscilloscope38 of FIG. 1 indicating, by cathode ray tube (CRT) display, reflectionsof electromagnetic energy from pipeline liquids that have seeped intotransmission'line 26. Electromagnetic discontinuities in thetransmission line 26 are indicated by response spikes 46a, 46b and 460.The oscillogram can be permanently recorded by photographing the CRTdisplay using a camera, or can be permanently recorded using aconventional X-Y recorder connected to the output of the oscilloscope38. The vertical channel of the oscilloscope 38 is usually calibrated interms of reflection coefficients, the threshold level being establishedto detect intrusions of a particular liquid conveyed in the pipeline 10of FIG. 1 into the transmission line 26. In this regard, it should beevident that any transmission line may have reflection discontinuitiesassociated with it. For example, even a conventional coaxial componentsuch as a connector will createsome impedance mismatch with respect tothe line. However, only when the magnitude of the discontinuity is abovea selected threshold level will the oscilloscope 38 be actuated. It hasbeen found that if the liquid within the pipeline 10 is an oil orpetroleum product, rather high reflection coefficients will be presentalong thetransmission line 26. Itcan be appreciated that the grid linesa, b...k of the oscillogram 45 directly relate to the distanceseparating the discontinuities relative to the geometric position of theoscilloscope. Below threshold, the signal output of the oscilloscope isdisplayed as a flat horizontal line 47. Further, the CRT display of theoscilloscope can be calibrated to represent many magnitudes of actuallength of pipeline. The distance/horizontal scale of the oscilloscope iscalibrated along axis 48 of FIG. 4 to relate horizontal dimensions ofthe CRT display to the actual dimensions separating discontinuitiesalong the transmission line 26 with respect to the actual known positionof the reflectometer.

Higher frequency systems can also be used in the method of the presentinvention in order to increase the resolution of the reflectometersystem. In this regard it should be understood that the transmissionline of the present invention supports travel of two traveling waves. Anincident traveling wave travels down the line and is reflected in partfrom discontinuities therealong when it encounters an impedance otherthan theimpedance of the line which it travels. Standing waves are thenset up on the line on the input side of the reflecting impedance. Themagnitude and phase of the reflecting will depend upon the amplitude andphase of the reflecting impedance. The reflected wave on a transmissionline may be considered as the fraction of the incident wave that isreflected from the load impedance and. carries that fraction of powernot absorbed by the load impedance from the incident wave. In highfrequency systems, the reflectometer can be a more conventionalclosed-loop radar system operating in either the time or frequencydomain and including a conventional generator/modulator connected to acompatible transmission line through a switching duplexer. A receiver isconnected in series with the duplexer to detect reflections fromdiscontinuities along the transmission line. Since the pulse width a canbe reduced, resolution of reflections from closely adjacentdiscontinuities is increased. Display of the reflections can be inconventional manner using an oscilloscope similar to that illustrated inFIGS. 1 and 4.

FIG. 5 illustrates a modified form of a high-frequency reflectometersystem. In the FIG., the time domain reflectometer 50 includes a pulsegenerator 51 for generating a pulse signal. Generator 51 is triggered bymeans of a synchronizing signal from a conventional time base 52connected to and triggering sampling oscilloscope 53. In operation, apulse of high frequency electromagnetic energy is driven through ahigh-frequency trigger countdown 58 and sampler 55 into the buriedrectangular waveguide 54 through switch 56, such as a ferromagneticallycontrolled Magic Tee, and propagates along the guide adjacent to theburied pipeline. As the energy strikes the discontinuities (markingintrusions of pipeline liquid), signals are reflected back through thesampler 55 through a vertical amplifier 57 and thence to oscilloscope53. The resulting reflections aredisplayed on the oscilloscope producingan amplitude-versus-time oscillogram.

It has been found that high frequency reflectometer system having thefollowing components is of particular utility in the frequency range ofl to 12.4 Gl-lz.:

Resolution of the above-described reflectometer system can be as high as1 cm. per unit length of transmission line. Reflection coefficientsensitivity to 0.002 per cm. of transmission l line can also be observed(see technical bulletin entitled, I-IP A] 141 Plug-in Oscilloscope,"July 1967, Hewlett- Packard Corp. Palo Alto, Calif. at page 22).

Similarly, it has been found that a reflectometer system having thefollowing identification can also be used: cable Fault Locator Model 110A, Jerrold Electronics Corp., Government and Industrial Division, 401Walnut St., Philadelphia, Pa.

FIG. 6 illustrates rectangular waveguide 54 in more detail. As shown,waveguide 54 is of rectangular cross section and includes metallicsidewalls 59 and 60 connected, at ends, to metallic broad walls 61 and62. Sidewalls 59 and 60 as well as broad walls 61 and 62 are perforatedwith a series of openings generally indicated at 63. An outer covering,sheath, 64 of insulating material is placed in contact with the exteriorsurfaces of walls 59, 60, 61 and 62 of the waveguide. Dimensions of theside and broad walls of the waveguide are selected to propagatehigh-frequency electromagnetic energy. As previously discussed, theouter covering 64 must have the capability to allow intrusion of aliquid from the pipeline to be monitored therethroughJn that .way theliquid can penetrate the cavity 65 at the axis of symmetry 66 of thewaveguide and create an abrupt change in the transmission characteristicof the waveguide. in order that the outer covering 64 allow intrusion ofthe liquid from the pipeline but exclude all other liquids commonlyfound within near-surface earth formation, the material forming thecovering must be carefully selected. In this regard, as previouslymentioned, outer covering 64 can be formed of asphalt materials,wax-based compositions, rubber-based (oil-soluble) compositions orsynthetic (oil-soluble) polymers if the liquid within the pipeline is anoil or oil product. Further, if the waveguide is used in the permafrostregions of the world, the covering can also be formed of cellulose,carbowax or guar gum materials.

While certain preferred embodiments of the invention have beenspecifically disclosed, it should be understood that the invention isnot limited thereto as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

We claim:

1. The method of forming a pipeline and communication line link whichconsists of the steps of:

l. laying a pipeline and electromagnetic transmission line together intandem relationship as between pumping and discharge stations, saidtransmission line having an electrically insulating outer coveringformed of a material soluble in a liquid to be conveyed in said pipelineand conducting means for propagating electromagnetic energy along saidtransmission line,

2. connecting said pipeline, at one end, to a source of said liquid,and, at the other end, connecting said pipeline to a discharge terminal,

3. selectively connecting said conductingmeans of said transmission lineto one of (a) an electromagnetic reflectometer system and (b) adirect-line, two-way communication system, so that when saidtransmission line is con nected to said reflectometer system seepage ofsaid liquid from said pipeline through flaws in said pipeline intopositions within said transmission line can be indicated and identifiedby measuring the two-way travel time of electromagnetic energy to andfrom said positions of said seepage in said transmission line and whensaid transmission line is connected, in direct line linkage, to saidcommunication system, information can e conveyed from location alongsaid transmission line.

2. Method of claim 1 in which the step of laying said pipeline and saidelectromagnetic transmission line, is further characterized by locatingsaid transmission line at a depth below said pipeline.

3. The method of claim 2 in which the step of locating said transmissionline below said pipeline includes laying said transmission line intangential contact with said pipeline.

4. The method in accordance with claim 1 with the additional step ofmonitoring signal amplitude when said conducting means of saidtransmission line is connected to said communication system so as toinitially indicate deterioration in signal level along said transmissionline.

5. The method of claim 1 in which said pipeline and said transmissionline are buried in an earth formation of a permafrost region, saidelectrically insulating covering means of said transmission line beingcomposed of a material soluble both in said liquid to be conveyed insaid pipeline and in water. i

6. The method of locating flaws in a buried, hollow pipeline using atime-sharing transmission line, which comprises the steps of:

a. positioning adjacent to said pipeline, a transmission line havingconducting means and electrically insulating covering means soluble in aliquid to be conveyed in said pipeline and located exterior of saidconducting means, said conducting means being capable of propagatingelectromagnetic energy therealong and to indicate, by measurement of thetwo-way travel time of generated and reflected energy, locations ofelectromagnetic discontinuities along said transmission line from aknown point, said transmission line being positioned so that said liquidbeing conveyed in said pipeline and seeping from flaws in said pipelinecan enter into said transmission line through said covering means, intocontact with said conducting means,

. Generating and receiving along said transmission line, in-

cident and reflected electromagnetic signals by means of at least firstand second electromagnetic generating and receiving systems directlyconnected to said conducting means of said transmission line, eachsystem having at least a transmitter and a receiver,

c. utilizing, over a first preselected time interval, said reflectedelectromagnetic signals to indicate the condition of said pipeline as tothe presence and absence of flaws therealong, the magnitude of saidreflected signals above a selected threshold level indicating theoccurrence of leakage of said liquid from said pipeline, and

d. thereafter utilizing, over a second time interval, said incidentelectromagnetic signals conveying meaningful information from atransmitter of one of said first and second electromagnetic generatingand receiving systems to a receiver of the other of said first andsecond electromagnetic generating and receiving systems, therebyproviding direct-line communication between said first and secondgenerating and receiving systems.

7. The method in accordance with claim 6 in which the step of utilizingsaid reflected electromagnetic signals, over said first time interval,includes the substep of monitoring an electrical characteristic of saidreflected energy whereby the magnitude of said characteristic above aselected threshold level indicates the existence of said liquid withinsaid transmission line and hence the occurrence of leakage from saidpipeline of said li uid.

8. e method in accordance with claim 7 including the substep ofmonitoring the two-way travel time between generated and reflectedelectromagnetic signals of one of said first and second generating andreceiving systems so as to pinpoint the distance between said liquidwithin said transmission line and a point of known location along saidtransmission line at which said one of said first and second generatingand receiving systems is positioned.

9. The method in accordance with claim 7 in which said substep ofmonitoring said electrical characteristic is further characterized byselectively indicating only reflected signals proportional to a selectedreflection coefficient greater than a threshold reflection coefficient,said threshold reflection coefficient being selected whereby themagnitude thereof indicates intrusions of said liquid from said pipelineinto said transmission line.

1. The method of forming a pipeline and communication line link whichconsists of the steps of:
 1. laying a pipeline and electromagnetictransmission line together in tandem relationship as between pumping anddischarge stations, said transmission line having an electricallyinsulating outer covering formed of a material soluble in a liquid to beconveyed in said pipeline and conducting means for propagatingelectromagnetic energy along said transmission line,
 2. connecting saidpipeline, at one end, to a source of said liquid, and, at the other end,connecting said pipeLine to a discharge terminal,
 3. selectivelyconnecting said conducting means of said transmission line to one of (a)an electromagnetic reflectometer system and (b) a direct-line, two-waycommunication system, so that when said transmission line is connectedto said reflectometer system seepage of said liquid from said pipelinethrough flaws in said pipeline into positions within said transmissionline can be indicated and identified by measuring the two-way traveltime of electromagnetic energy to and from said positions of saidseepage in said transmission line and when said transmission line isconnected, in direct line linkage, to said communication system,information can e conveyed from location along said transmission line.2. connecting said pipeline, at one end, to a source of said liquid,and, at the other end, connecting said pipeLine to a discharge terminal,2. Method of claim 1 in which the step of laying said pipeline and saidelectromagnetic transmission line, is further characterized by locatingsaid transmission line at a depth below said pipeline.
 3. The method ofclaim 2 in which the step of locating said transmission line below saidpipeline includes laying said transmission line in tangential contactwith said pipeline.
 3. selectively connecting said conducting means ofsaid transmission line to one of (a) an electromagnetic reflectometersystem and (b) a direct-line, two-way communication system, so that whensaid transmission line is connected to said reflectometer system seepageof said liquid from said pipeline through flaws in said pipeline intopositions within said transmission line can be indicated and identifiedby measuring the two-way travel time of electromagnetic energy to andfrom said positions of said seepage in said transmission line and whensaid transmission line is connected, in direct line linkage, to saidcommunication system, information can e conveyed from location alongsaid transmission line.
 4. The method in accordance with claim 1 withthe additional step of monitoring signal amplitude when said conductingmeans of said transmission line is connected to said communicationsystem so as to initially indicate deterioration in signal level alongsaid transmission line.
 5. The method of claim 1 in which said pipelineand said transmission line are buried in an earth formation of apermafrost region, said electrically insulating covering means of saidtransmission line being composed of a material soluble both in saidliquid to be conveyed in said pipeline and in water.
 6. The method oflocating flaws in a buried, hollow pipeline using a time-sharingtransmission line, which comprises the steps of: a. positioning adjacentto said pipeline, a transmission line having conducting means andelectrically insulating covering means soluble in a liquid to beconveyed in said pipeline and located exterior of said conducting means,said conducting means being capable of propagating electromagneticenergy therealong and to indicate, by measurement of the two-way traveltime of generated and reflected energy, locations of electromagneticdiscontinuities along said transmission line from a known point, saidtransmission line being positioned so that said liquid being conveyed insaid pipeline and seeping from flaws in said pipeline can enter intosaid transmission line through said covering means, into contact withsaid conducting means, b. Generating and receiving along saidtransmission line, incident and reflected electromagnetic signals bymeans of at least first and second electromagnetic generating andreceiving systems directly connected to said conducting means of saidtransmission line, each system having at least a transmitter and areceiver, c. utilizing, over a first preselected time interval, saidreflected electromagnetic signals to indicate the condition of saidpipeline as to the presence and absence of flaws therealong, themagnitude of said reflected signals above a selected threshold levelindicating the occurrence of leakage of said liquid from said pipeline,and d. thereafter utilizing, over a second time interval, said incidentelectromagnetic signals conveying meaningful information from atransmitter of one of said first and second electromagnetic generatingand receiving systems to a receiver of the other of said first andsecond electromagnetic generating and receiving systems, therebyproviding direct-line communication between said first and secondgenerating and receiving systems.
 7. The method in accordance with claim6 in which the step of utilizing said reflected electromagnetic signals,over said first time interval, includes the substep of monitoring anelectrical characteristic of said reflected energy whereby the magnitudeof said characteristic above a selected threshold level indicates theexistence oF said liquid within said transmission line and hence theoccurrence of leakage from said pipeline of said liquid.
 8. The methodin accordance with claim 7 including the substep of monitoring thetwo-way travel time between generated and reflected electromagneticsignals of one of said first and second generating and receiving systemsso as to pinpoint the distance between said liquid within saidtransmission line and a point of known location along said transmissionline at which said one of said first and second generating and receivingsystems is positioned.
 9. The method in accordance with claim 7 in whichsaid substep of monitoring said electrical characteristic is furthercharacterized by selectively indicating only reflected signalsproportional to a selected reflection coefficient greater than athreshold reflection coefficient, said threshold reflection coefficientbeing selected whereby the magnitude thereof indicates intrusions ofsaid liquid from said pipeline into said transmission line.